This invention relates to a hermetically sealed motor compressor unit of the type having refrigerant gas at discharge pressure substantially surrounding the motor of the unit, and in particular, relates to apparatus and method for controlling the performance characteristics of the compressor.
It has been found that the energy efficiency of a motor compressor unit can be significantly increased by filling the chamber in which the motor compressor unit is mounted with refrigerant gas at discharge pressure. Heretofore, it has been the practice to fill the chamber with gas at suction pressure, with the gas cooling the motor's windings prior to entry into the compressor's cylinders. In the present arrangement, the suction gas is not used for motor cooling, but rather is led to a relatively small chamber or plenum in direct flow communication with the compressor's cylinder. The temperature of the gas is thus maintained at a minimum prior to compression.
In addition to the foregoing, it has also been recognized that improvements in the energy efficiency of a compressor may be obtained by insuring that the suction valve closes and is prevented from opening when the piston in a cylinder is compressing gas therein to avoid any backflow of gas from the cylinder to the suction plenum. It is further desirable for improving efficiency to insure that the pressure in a suction plenum is at a maximum when the suction valve opens to cause a maximum flow of gas into the cylinder for compression.
Since, in a hermetically sealed compressor having discharge gas surrounding the motor, the suction gas, of necessity, is led directly into the suction plenums surrounding the cylinders of the compressor, it has been found advantageous to interconnect the various conduits delivering refrigerant gas to each suction plenum to achieve optimum control of the opening and closing of each cylinder's suction valve. In addition to interconnecting the suction conduits to control the compressor's performance, it has been found that compressor performance will be affected by the volume of the suction plenum and by the length and diameter of the interconnected conduits. In fact, it has been found that the particular length of the conduits should be varied in accordance with design changes in the volume of the suction plenum and/or diameter of the conduits for obtaining desired performance characteristics for the compressor.
In automotive engines, it is known that improved performance may be obtained by providing discharge lines of varying length from the cylinders to rapidly achieve a maximum flow of discharge gas from the engine. It is also known in the automotive engine art to vary the length of suction lines for supercharging air into the engine's cylinders. However, as is readily recognized, automotive engines use mechanical valve lifters for controlling the movement of the suction and discharge valves. No similar devices are employed in hermetically sealed compressors wherein it has been found that pressure pulsations within interconnected conduits communicating the various suction plenums of the compressor can be controlled and used to achieve desired performance characteristics for the compressor.